1. Field of the Invention
The present invention relates to a spin transport device using magnetic fields.
2. Related Background Art
Spin transport devices have been attracting the attention recently. As it had been conventionally believed that a flow of spins (spin current) is associated with an electric current, a flow of spins alone was previously unknown. A spin current associated with an electric current is utilized for broad product applications generally utilizing magnetoresistance effects. Such products include magnetic heads for hard disk drives (HDDs), magnetic sensors or magnetoresistive random access memories (MRAMs). Devices utilizing a conventional spin current associated with an electric current and devices utilizing a spin current alone are collectively called as spin transport devices.
Spin transport devices utilizing thin-film technology have also been attracting the attention. One of applications thereof is Spin-MOSFET (see Japanese Patent No. 4143644, Japanese Patent Application Laid-open No 2002-246487 and Japanese Patent Application Laid-open No. H09-097906). Other technologies relating to spin currents are described in, for example, Japanese Patent No. 3818276 and F. J. Jedema et. al., “Electrical detection of spin precession in a metallic mesoscopicspin valve”, Nature, 416, 713, (2002).
However, when spins travel a long distance, the direction of spins may be easily affected by external magnetic fields. In such case, spins are forced to rotate even with a weak external magnetic field, resulting in modification during transmission of otherwise accurate magnetization information which depends on the direction of spins. Spins possess magnetization information at the initial stage of transmission, which depends on the magnetization direction of a ferromagnetic substance through which spins pass at the initial stage. When magnetization information modified during transmission is collected, accurate information is decreased and noise information is increased. Generally, increase in noise information is not preferred.
On the other hand, new technology may be developed if such adverse effect as modification of magnetization information could be exploited positively. However, it has been believed that it is impossible to exploit the phenomenon of modification of magnetization information, i.e. “Hanle effect”, in a positive way because in order to induce “Hanle effect” for rewriting information, an external magnetic field perpendicular to the transmission direction of spins and to the magnetization direction of spins needs to be applied, while deviation of the external magnetic field from the perpendicular direction causes uneven rotation of spins relative to the external magnetic field; due to these, it may be difficult to accurately rewrite the information.